In many areas of measuring technology and data acquisition, a desired wanted signal is superimposed with an undesired disturbing signal. This phenomenon is generally referred to as interference. It is often not possible to achieve an adequate reduction in the effect of the disturbing signal by suitable modification of the physical measuring conditions. In such cases, it is attempted to compensate for the interference after the data acquisition by methods of adaptive digital signal processing in the measurement signal with the incorporation of a reference signal of the disturbance (interference compensation). A particular difficulty occurs if significant proportions of the disturbance are not contained in the reference signal. In such cases, the known processes for adaptive interference compensation fail.
FIG. 1 shows in a diagrammatic way the previously known approach to interference compensation (B. Widrow and S. D. Stearns: "Adaptive Signal Processing", Prentice-Hall, Englewood Cliffs, N.J., 1985). In the case of these known processes, it is assumed that an "observation" of the disturbing signal is available in the form of a reference signal n'. An adaptive filter forms a linear or nonlinear combination of a number of temporally successive values of the reference signal n'. This adaptively preprocessed reference signal is then subtracted from the disturbed measurement signal s+n. The parameters of the linear or nonlinear adaptive filter are in this case set such that the energy of the output signal E assumes a minimum. Consequently, the disturbing signal component in the output signal is minimized in accordance with the method of least squares (B. Widrow 1985).
The classical approach to interference compensation hereby described is based on the implicit assumption that all the components of the interference can be represented by suitable linear or nonlinear compensations of a reference signal. The classical approach fails, or supplies inadequate compensation results, if this prerequisite is not met, i.e. if significant components of the disturbance are not depicted in the reference signal.